Cholesterol and cholesterol esters, both of which are designated in the following as cholesterol, are lipophilic substances which occur in numerous important foodstuffs of animal origin, for example egg yolk, meat, animal fats and the like.
As is known, increased cholesterol levels in the blood serum of humans represent an increased risk factor for arteriosclerosis and for coronary heart disease.
By means of a reduction of the cholesterol intake, it is, in most pathological cases, possible again to achieve the normal cholesterol levels in blood serum. For this reason, an important endeavour of the foodstuff industry is to carry out a marked reduction of the cholesterol in fat-rich foodstuffs of animal origin.
An important problem is thereby the substantial maintenance of the sensory and nutritional-physiological properties of the foodstuffs.
According to the prior art, admittedly a number of processes are known for the isolation of cholesterol but, because of the chemical change of important components of the starting material, for example of proteins, triglycerides and the like, these methods are not suitable for the reduction of the cholesterol content of foodstuffs.
A relatively gentle process which has only become known recently uses carbon dioxide high pressure extraction for the removal of cholesterol (cf. V. Krukonis, Supercritical Fluid processing, International Symposium on Supercritical Fluids, Nice, 1988).
This process is admittedly characterised by the physiological harmlessness of the extraction agent, carbon dioxide, but working at a high pressure is technically somewhat laborious. Furthermore, according to this process, cholesterol cannot be removed selectively under gentle conditions because triglycerides are also extracted at the same time. An improvement of the selectivity by increasing the temperature is admittedly possible in principle but this has a negative effect on the loading of the carbon dioxide with cholesterol and on the quality of the product obtained.
Another known process for the removal of cholesterol derivatives is the complexing of these substances with .beta.-cyclodextrin. Thus, for example, according to published European Patent Specification No. 0,326,469, egg yolk powder, after homogenization thereof with water, is stirred for 5 hours at 40.degree. C. with .beta.-cyclodextrin and the complex obtained is separated by centrifuging. In this way, however, the cholesterol contents can only be reduced to at most 74% of the initial values.
According to the process described in copending U.S. application Ser. No. 439,556, filed Nov. 21, 1989, exclusively, the egg yolk plasma, which has been obtained from egg yolk with the help of an emulsion-breaking agent (water) after centrifuging off the LDL granula fraction, is mixed with .beta.-cyclodextrin. Subsequently, after separating the .beta.-cyclodextrin, the egg yolk plasma treated in this manner is again combined with the LDL granula fraction. However, in some cases, the separation of the egg yolk plasma from the LDL granula fraction and from the .beta.-cyclodextrin-cholesterol complex gives rise to difficulties.